In recent years, hydrogen has been found to have the effect of removing active oxygen, which is thought to cause aging and cancer. It is also reported that, when drinking water containing hydrogen, it is possible to remove active oxygen in the body and to remedy health impairments, such as allergic diseases and digestive diseases. The use of water having hydrogen dissolved therein (hereinafter, referred to as hydrogen water) as a drink in consideration of the fact that hydrogen has the effect of removing active oxygen as described above has attracted considerable attention. In fact, the market for hydrogen water for drinking has quickly expanded.
It is generally thought that, when the concentration of hydrogen contained in hydrogen water is high, the hydrogen water has the effect of removing active oxygen. For this reason, the amount of hydrogen that is contained in hydrogen water is important in showing the effect of the hydrogen water. Consequently, it is considerably important to know the concentration of hydrogen in hydrogen water, i.e. the concentration of hydrogen molecules contained in an aqueous solution (hereinafter, referred to as dissolved hydrogen).
In general, however, no clear criterion is prescribed for a method of measuring the concentration of dissolved hydrogen (such a criterion is not prescribed even in, for example, JIS standards). In addition, in a conventional method of measuring the concentration of dissolved hydrogen, the concentration of dissolved hydrogen is generally calculated on the basis of oxidation-reduction potential (for example, Patent Document 1). Consequently, all materials having an influence on oxidation and reduction are measured, and therefore it is not clear whether or not the concentration of only hydrogen dissolved in an aqueous solution is appropriately displayed.